In the practice of testing fluid samples, for instance the analysis of microbiological organisms in pharmaceutical, beverage, or environmental fluids being good examples, it is important that the fluid sample be handled in a manner that prevents it from becoming contaminated or adulterated with organisms or other substances extrinsic to the sample that could alter the outcome of the microbial test. This includes introduction of organisms from the external environment. A prime example is the testing of sterility of a parent fluid volume by removing a portion as a test sample. If the extracted fluid sample becomes contaminated in the analytical process through exposure to organisms that are not part of the parent fluid, then the outcome of the test will be flawed.
For testing purposes, it can be necessary to obtain the sample at one location that is the source of the parent fluid volume, and then convey the sample to another locale where the testing process takes place, such as in a test laboratory. This requires samples to be securely sealed in a vessel suited for transport, which will not leak, nor allow the contents to become contaminated in the transportation process. The fluid sample volume can vary in amount from microliters to liters, 100 mL being an exemplary volume for testing the microbial content for instance of water for human consumption.
Commonly used fluid sample vessels are glass and plastic bottles, usually sterilized for test applications involving the microbiological analyses. These have the disadvantage that their weight and typical rigidity make them costly to transport, and inconvenient to pack, ship and store. An alternative to this is a collapsible or flexible thin wall plastic containment vessel, a preferred case being in the form of a pouch or bag. The pouch or bag has the advantage of low cost, light weight, and space-saving for compact packaging. One bag design that is frequently used as a fluid sample vessel, called Whirl-Pak, employs a twisted-wire top closure that addresses the problem of creating a leak-proof seal for the filled container, without requiring a cap or fixed closure for the opening where the sample fluid is introduced.
Whether involving either rigid or flexible vessels, the container used for the initial collection, transport, and storage of the fluid, ultimately is opened in order to access the sample and remove all or some portion of the fluid upon which the analytical procedure is then performed. The opening of the vessel and the operation of extricating fluid for testing exposes the sample to the potential contaminants external to the vessel and the fluid sample.
For microbiological testing, one prevalent test type is a filtration process in which the sample is aspirated under vacuum through a porous membrane that captures the bacteria and removes the fluid. The procedure typically involves transferring fluid from the fluid-sample vessel to a filter-apparatus that consists of a vessel capable of holding the volume that is to be processed and a membrane filter (MF) constrained therein through which the fluid will be suctioned. The membrane filter is then exposed to bacterial-growth media and incubated in a culture vessel, which typically involves a physical manipulation of the MF to convert it from being in the filtration-processing state to being in an incubation condition.
An advantage offered by the membrane-filter assay method with respect to microbial analyses is that individual organisms can be captured from relatively large volume fluid samples and they can be cultured on or in the filter when it is exposed to a suitable growth medium and incubation temperature. The organisms proliferate and eventually form colonies that can be identified on the filter surface. The colony formations can be differentiated by bacterial type, and enumerated, thereby providing valuable information about the concentration of the parent organisms present in the fluid sample at the time of its filtration.
These sample-preparation procedures, from the point of getting fluid out of the fluid sample vessel, through the filtration process, and additionally into the assay and culture phase of analysis, involve a variety of manipulations on the part of the user. There are attendant opportunities for contamination through exposures of the fluid sample, or the substance removed from it, by the filtration process and the steps of preparation for the assay and incubation. Moreover, special equipment is needed and skilled personnel (trained in its usage as well as the laboratory procedures typically employed to minimize the risks of external contamination) are required. A significant amount of materials are used that come in contact with the sample, which after use must be treated as contaminated thereby either disposed of or disinfected, or both.
For these and other reasons, the analytical procedure is therefore typically performed in the clean environment of a well-equipped microbiological test laboratory. However, access to a lab setting and trained operators is often not practical and presents complications towards testing samples in many cases.